Mukhannath literally means a ‘feminized one’ and is used in Classical Arabic for people who were anatomically male in some way but more equivalent to women in other ways, behaviorally or anatomically. They became a special social category to themselves, like a third gender. In Modern Standard Arabic, the word is more narrowly used for intersex people specifically.

Mukhannathūn are not mentioned directly by Allāh in the Qurʾān. We do however have a few traditional reports of how the Prophet Muḥammad ﷺ interacted with feminized Muslims:

Ḥadīth of the henna-adorned Mukhannath

In this case, the Mukhannath’s behaviour and presentation were feminine, but apparently not her anatomy.

This made the men uncomfortable, and she was asked to leave their community.

It was explicitly forbidden to kill her.

Classical scholars

[Found in Wikipedia.... unverified source!]

Imām al-Nawawī discusses feminized ones:

A Mukhannath is the one [born male] who carries in their movements, in their appearance and in their language the characteristics of a woman. There are two types:

The first is the one in whom these characteristics are innate, they did not put them on by themself. Therein is no guilt, no blame and no shame, as long as they do not perform any lewd act or exploit it for money.

The second type acts like a woman out of immoral purposes. They are the sinner and blameworthy.